A switch-mode power supply (also known as a switch-mode converter) is an electronic circuit that converts an input direct current (DC) voltage into one or more DC output voltages that are higher or lower in magnitude than the input DC supply voltage. A switch-mode power supply that generates an output voltage lower than the input voltage is termed a buck or step-down converter. A switch-mode power supply that generates an output voltage higher than the input voltage is termed a boost or step-up converter.
A typical switch-mode power supply includes a switch for alternately opening and closing a current path through an inductor in response to a switching signal. In operation, a DC voltage is applied across the inductor. Electrical energy is transferred to a load connected to the inductor by alternately opening and closing the switch as a function of the switching signal. The amount of electrical energy transferred to the load is a function of the duty cycle of the switch and the frequency of the switching signal. Switch-mode power supplies are widely used to power electronic devices, particularly battery-powered devices, such as portable cellular phones, laptop computers, and other electronic systems in which efficient use of power is desirable.
Switch-mode power supplies are sometimes provided in modular form, where a sealed assembly of electronic components provides the converter functionality.